1. Field of the Invention
Embodiments of the present invention relate generally to disk drives and methods and, in specific embodiments, to a disk drive including a servo controller for controlling a movement of an actuator based on a super silent seek profile to cause the actuator to perform a super silent seek in which an acoustic output due to the movement of the actuator is imperceptible to human listeners.
2. Related Art
Disk drives are widely used in computers and other electronic devices for the storage and retrieval of data. In the past, there has been a great focus on improving disk drive performance by minimizing seek time during reads and writes. As a result, seek operations have traditionally been performed as quickly as possible. More recently, there has been a recognition that when the mechanical components of a disk drive are moved as quickly as possible to minimize seek time, acoustic noise is generated that can be annoying and even worrisome to end users. Some attempts have been made in related art disk drives to reduce the amount of acoustic noise generated during seeks. However, in the related art disk drives, some amount of acoustic noise is still generated during seek operations that is perceptible and noticeable to human listeners, which has led to end user dissatisfaction with the disk drives.
In general, related art disk drives comprise one or more disks for storing data, an actuator, one or more transducers or heads, and a servo controller. Each head is operable to read data from and to write data to one or more tracks on a surface of a corresponding disk. The tracks are typically concentric circular tracks, but a disk may have a spiral track, such as is common for compact discs (CDs). The heads are connected to the actuator, and when a head performs a read or a write operation on a disk, the actuator is moved as part of a seek operation so that the head is positioned over a destination track. The movement of the actuator during a seek operation is controlled by the servo controller based in part on a seek profile that specifies how the actuator is to be moved during the seek operation.
In order to maximize disk drive performance, disk drive manufacturers have generally sought to minimize seek time by employing a seek profile known as a performance seek profile or a bang-bang seek profile. Such a performance seek profile is described in U.S. Pat. No. 4,937,689 entitled “Apparatus for Controlling Seek Strategy of Read/Write Head in a Disk Drive”, the contents of which are incorporated by reference herein, and which is hereinafter referred to as reference 1. In FIG. 2 of reference 1, there is shown an example of a performance seek profile in which: (i) at time t0, a head is subjected to instantaneous maximum acceleration Am; (ii) the maximum acceleration is held until the head reaches a maximum velocity Vm at time tm; and (iii) the maximum velocity is held until time (tn-tm) at which time the head is subjected to maximum deceleration −Am so that the velocity linearly decreases to zero at time tn.
Such a performance seek profile has come to be known as a bang-bang seek profile, because the actuator first moves the head with maximum acceleration, and then later moves the head with maximum deceleration. By controlling the actuator to move the head with maximum acceleration and deceleration, noticeable levels of acoustic noise are generated due to vibration introduced to an actuator arm assembly on which the head is mounted as a result of the instantaneous acceleration and deceleration by the actuator. Performance seeks also have an issue with settling time, as they cause the actuator to decelerate fast, and there is no assurance that the head will settle in a stable manner over the destination track. In general, with performance seek profiles, there is very often an overshoot of the destination track, and time is required for recovery from the overshoot.
In order to reduce an amount of acoustic noise that is generated during seek operations, various related art disk drives have been designed to employ silent seek profiles or quiet seek profiles or low-noise seek profiles that result in less acoustic noise being generated than when performance seek profiles are employed for seek operations. Examples of related art disk drives that employ silent seek profiles are described in the following references: (i) reference 1; (ii) U.S. Pat. No. 6,624,964 entitled “Method and Apparatus for Reducing Seek Acoustics in Disk Drives for AV Systems”, the contents of which are incorporated by reference herein, and which is hereinafter referred to as reference 2; and (iii) U.S. Pat. No. 6,396,653 entitled “Apparatus and Method for Reduction of Idle-Mode Acoustics in a Disc Drive”, the contents of which are incorporated by reference herein, and which is hereinafter referred to as reference 3.
In reference 1, noise is reduced during seek operations in a disk drive by providing seek profiles that allow for controlling seek operations in which a head is gradually accelerated and then gradually decelerated to move the head from one track to another. The gradual acceleration/deceleration of the head, as performed in reference 1, was found to reduce noise and system wear as compared with the full-power and instantaneous acceleration/deceleration of a bang-bang seek profile.
However, in reference 1, the proposed seek profiles begin with an acceleration of 0, and then start acceleration in accordance with a linear function given by A(tn)=Jt, where J=the increase in acceleration per time sample, and t=the number of samples. Thus, the derivative of acceleration, which is known as jerk, immediately changes from a value of 0 to a fixed value of J at the beginning of seek operations, so the change in jerk is not smooth. The derivative of jerk is known as snap, and the value of snap when the jerk changes immediately from 0 to the fixed value J, is infinite. Also, in the seek profiles of reference 1, when the acceleration reaches a target acceleration after increasing according to a linear function, the acceleration becomes constant. Thus, the jerk changes immediately from the fixed value J to 0, and the absolute value of the snap at that time is again infinite. Therefore, while reference 1 is concerned with decreasing velocity and providing for gradual acceleration, reference 1 does not allow for placing a limit on snap, so a rate of change of jerk can be great.
In reference 2, there is noted a disadvantage of conventional disk drives in that the velocity profile of such conventional disk drives are designed to minimize access time for random seeks, which is particularly problematic when the disk drives are utilized for storage of Audio Visual/Video (AV) content in AV systems such as consumer electronics (e.g. Digital Video Recorders) in which access patterns require non-random seeks that generate significantly higher acoustic noise than random seeks. In order to reduce acoustic noise for seek operations, reference 2 discloses disk drives in which a seek profile for a seek operation depends on a seek length (i.e. distance between starting and destination tracks), and a current value and a target velocity can differ among seek profiles for different length seeks. However, similar to reference 1, while reference 2 focuses on reducing current and velocity, reference 2 does not disclose placing a limit on snap, so a rate of change of jerk can be great.
In reference 3, there is proposed a low-noise velocity profile that adjusts the acceleration, maximum velocity, and deceleration of an actuator to reduce the noise generated by the movement of the actuator during seeking. In the disk drives of reference 3, the low-noise velocity profile may be automatically used during idle periods for internal housekeeping operations of the disk drives, such as maintenance or self-diagnostic seeks, and may be automatically used for seek commands that come from a source other than a user, such as seek commands from a network. However, the disk drives of reference 3 only allow for an automatic use of the low-noise velocity profile, and do not allow for receiving a command from external sources to selectively enable and disable the use of the low-noise velocity profile. Also, the disk drives in reference 3 have no way to distinguish between seek operations initiated by an operating system and seek operations initiated by a user. Furthermore, the seek profiles disclosed in reference 3 allow for rapid changes in acceleration and, thus, both a jerk and a snap of the seek profiles may be great.
Even when employing the silent seek profiles or low-noise velocity profiles of the related art disk drives, a noticeable amount of noise is still produced during seek operations. For example, when silent seek profiles such as those described in the references are used for seek operations, there may be a level of noise generated during the seek operations that reaches more than 25 decibels (dB). Such an amount of generated noise may not be noticed by human listeners if there is some level of surrounding ambient noise, but the human ear can hear sound at levels as low as 18 dB, so such generated noise during seek operations may be perceived and noticed when there is a low level of surrounding ambient noise.
For example, if a user of a computer with a disk drive leaves the computer on in a room where the user is trying to sleep, there may be very low ambient noise in the room. Then, if the disk drive begins performing internal housekeeping operations, such as maintenance or self-diagnostic seeks, while the user is trying to sleep, the user may be very sensitive to any perceptible, extraneous, and uncontrolled noise and, thus, may be very annoyed that the disk drive is generating a noticeable amount of acoustic noise. Similarly, if a user in a quiet office is trying to concentrate or meditate, and is in deep thought, the user may become frustrated if a disk drive begins generating acoustic noise that is noticeable and interrupts the user's thought process. Also, there is a similar problem with audio CD systems, where changing a current audio piece causes audible noise when the CD head, which may be a mirror, is suddenly repositioned.
Moreover, if a user notices acoustic noise from a disk drive when the user has not performed an operation involving the disk drive, such as when the disk drive performs self-initiated internal housekeeping operations, the user may become worried and think that the disk drive has failed. Such worry or concern may be for no good reason, and may eventually lead the user to wrongly believe that the disk drive is defective and to return the disk drive. Thus, perceptible noise during seek operations may lead end users to lose confidence in the reliability and general health of their disk drives.
The disk drives of the related art continue to generate perceptible noise even when employing silent seek profiles, because such silent seek profiles focus on reducing velocity and adjusting acceleration, without focusing on reducing jerk and snap. A significant part of noise production in disk drives can be attributed to percussions that are due to rapid changes in jerk during a movement of an actuator. Even though the related art disk drives allow for adjusting acceleration for silent seek profiles, the related art disk drives do not impose a limit on a maximum amount of snap during seek operations, and, thus, do not ensure that the jerk during seek operations is smooth with no rapid changes. Jerks cause a percussion effect that can be perceived, especially in a quiet environment, while the movement of the actuator arm over the disk causes windage. Thus, the related art disk drives have not adequately addressed the contribution of jerk and snap to the acoustic noise that is generated during seek operations. The rotation of the disk also creates noise due to windage, which further contributes to the overall noise level produced by the disk drive.
Furthermore, in the related art disk drives, there is no way for a user or an operating system to issue a command to a disk drive to specify whether the disk drive should perform seek operations in accordance with a performance seek profile or a silent seek profile. Instead, in the related art disk drives, the use of the silent seek profile is automatic in various situations, such as for seek operations with a short seek length, for internal housekeeping operations, and for seek commands issued from specific sources. Thus, in the related art disk drives, there has not been an opportunity for a user or an operating system to specify whether a particular seek operation is to be performed with a performance seek profile or with a silent seek profile. Also, the related art disk drives do not allow for a user or an operating system to issue a command to select from among different types of seek profiles for particular seek operations, where each profile provides a different tradeoff between a speed of the seek operations and an acoustic output of the seek operations. While related art disk drives do provide a general setting to have all seeks done with a particular seek profile, such a general setting is not fine enough to be acceptable, especially because it takes a fair amount of time to come out of a silent seek mode in the related art disk drives where a silent seek profile is used for all seeks.
In light of the above mentioned problems, there is a need for disk drives with seek profiles that allow for reducing the amount of acoustic noise generated during seek operations, so that the acoustic noise generated during seek operations is not perceptible to human listeners. Also, there is a need for allowing disk drives to receive commands from users, operating systems, and the like that allow for selecting from among different modes for performing particular seek operations in which different seek profiles are employed.